Electrostatic machine



Oct. 20, 1953 N. FELlCl 2,656,502

ELECTROSTATIC MACHINE Filed NOV. 2, 1950 2 Sheets-Sheet l Zq 6 x ADJUSTABLE 6 p 62 cm 0/5 CHA 266 .05 VICE .NVENTOR l0 Nqel Flici ATTORNEY Oct. 20, 1953 N. FELICI 2,656,502

ELECTROSTATIC MACHINE Filed Nov. 2, 1950 T 2 Sheets-Sheet 2 INVENTOR Noel Felici ATTORNEY Patented Oct. 20, 1953 ELECTROSTATIC MACHINE Nol Felici, Grenoble, France, assignor to Centre National de la Recherche Scientifique, Paris, France, a corporation of France Application November 2, 1950, Serial No. 193,626 In France November 9, 1949 13 Claims. 1

The present invention relates to new means for maintaining the voltage of electrostatic generators practically constant, that is, practically independent of the intensity of the current delivered by such generators.

It is well known that electrostatic generators are inherently constant current generators while electromagnetic generators are more nearly constant voltage generators. Accordingly, when the exciting voltage is constant and in the absence of leaks and stray capacities the charge delivered by the transporter or carrier members of an electrostatic generator is a constant and, when rotation speed is constant, the result is the production of a current having a constant intensity independent of the output voltage. Leaks and stray capacities have a more or less pronounced efiect on this result but the output voltage in all cases may vary considerably with a given current drawn from the machine.

Such a feature is quite unfavourable to the connection of electrostatic generators with certain receivers, such as electronic tubes, which necessitate a practically constant voltage across the tube only influenced to a relatively small degree by current output variations. In certain cases, such as that of Y-ray tubes, a voltage strictly independent of the output is very convenient for the user, as it makes it possible, for instance, to adjust separately the penetrating quality and the volume of the radiation.

Heretofore it only has been possible to obtain a constant voltage from electrostatic generators by means of quite complex devices comprising numerous electronic tubes and the efficiency of these devices was not high.

The object of the invention is to provide means for solving the above-mentioned problem by using extremely simple devices which, in most cases, are limited to one or more electrical members the characteristic curve of which showing the current as a function of the voltage presents a bend or elbow.

It has been discovered in accordance with the invention that the voltage across the terminals of an electrostatic generator may be made constant by inserting between each inductor or equipotential group of inductors of the generator and another element of the apparatus the potential of which is constant during the operation and is suitably related to the output voltage a special resistance device the characteristic curve of which must fulfill particular conditions.

If U is the voltage to be produced by means of a generator of the Toepler type assumed to comiii) prise only one inductor, one of its terminals being insulated from ground and at potential +U. and the other terminal being connected to the frame or to ground (zero potential), and if -V is the potential of the inductor, the current pro duced can be shown to be:

I=AVBU (1) A and B being coefiicients proportional to the rotational speed of the carrier of the machine relative to the inductor, A being of positive sign and B being usually but not necessarily also positive.

The inductor only maintains its potential V when such inductor is connected to a source of electricity which makes up for electric leakage. If I is the current produced by means of this source, assumed to be a small auxiliary electrostatic generator similar to the main generator and excited by the main generator by having its inductor member connected to the insulated terminal of the main generator, the current is expressed in the following equation:

A and B being two other coefiicients for the auxiliary generator similar to the above-mentioned coefficients A and B.

Let Z be the effective resistance of a special resistance device inserted between the inductor of the main generator at potential V and the insulated terminal, at potential +U, of the main generator. The differential resistance or increment of resistance of this device is the ratio of an increment of voltage across its terminals to the corresponding variation of the current flowing through the device. The potential difference across the terminals of the device is U-f-V and the variation (11 of the current flowing through the device is such that:

In most cases the inductor is well insulated and the entire output current of the auxiliary excitation generator is absorbed by the special resistance device, so that I and I may be considered as having the same value. From Equations 2 and 3, therefore,

From Equation 1 the following equation may be deduced:

dI::AdV-BdU (5 Therefore, in order that the output voltage U may be independent of the output current I 5 and of V, one must have dU:0 for 11%10 and. for (ii 0.

Substituting dU:0 in Equation 4:

ZBdV:dV (6) which condition is satisfied if 2A is difierent from 1 and whence it results, on the other hand, that B must have a sign difierent from Z, that is, in the exciter system the coefficient B must be negative if resistance Z is positive which is generally the case in practice.

Moreover, it is not possible that 2 be simply an ohmic resistance independent of I because, if the working point (U, I) is stable, it remains stable when U and I are divided by any factor. This is particularly the case of the oint (-0.0) and consequently there will be no tendency of the machine to leave this neutral condition, and thence, to be primed. It is necessary that Z be a. resistance which varies as a function of the potential difference applied across it, the value of such resistance being equal to 1/B' when the potential difference is .near U+V and equal ordinarily to a larger value, such as infinity, for lower values of such potential difference.

Thus, the electrostatic generator according to the invention capable of producing .a constant voltage U practically independent from the current produced comprises an inductor brought to a potential V by means of an auxiliary source or" electricity, such as an exciter generator, and special resistance'device having a volt ampere or resistance characteristic such that the resistance thereof eifective to determine current flow therethrough and potential dropacross the device decreases or increases as the potential difference across this resistance device tends to vary, such decrease or increase of the effective resistance beingsufficient and in such direction as correspondingly to vary the current flow through the device so that the potential difference across the device remains substantially constant. The resistance device is inserted between such inductor an equipotential group of such inductors and a member of the generator the potential of which is constant/during the operation of the generator, for instance, the insulated output terminal itself of said generator. In Equation 2 the coefficient 13' defines the ratio of the current produced by the auxiliary exciting source to the voltage'across the terminals of that source and is of opposite sign to Z. The special resistance is so chosen that the value Z is equal to l/B when the potential diiference applied across it is near U-i-V, and is larger, for example infinite, for lower values 'of the this potential difference.

In practical embodiments of the invention there may be used as the special resistance device an autonomous glow discharge device comprising, for example, at least one point and one plate the relative distance between which is adjustable and between which an electric glow discharge may take place, this device being connected in series with an ohmic resistance of such a value that when the discharge has been established in the device the effective resistance or the assembly is equal to 1/3.

Two embodiments of generators according to the invention are illustrated in the annexed drawings in which:

Fig. 1 is a perspective diagrammatic view of an electrostatic generator excited by a group of two ordinary Toepler machines exciting each other and of which only one produces output current, the whole forming a self-exciting assembly with a negative coeflicient B and a coeiiicient A equal to zero;

Fig. 2 is a similar view of a so-called double transfer generator, that is one in which a transporter or carrier member not only supplies to the output circuit electric energy of a given sign but also extracts from the output circuit a comparable quantity of electric energy of the opposite sign, as disclosed in U. S. Patent No.

In the device shown in Fig. l the main generator comprises an inductor I and a screen 2 each of which is'made of two parallel plates between and into register with which may be moved successively two transporter or carrier members 3 and 4 insulatedly mounted on a shaft 5. Carrier members 3 and 4 are connected to contacts 5 and '1 respectively of a commutator carried on shaft 5 and cooperating with two brushes 8 and g respectively connected to the grounded metal frame of the machine diagrammatically shown at [0 and forming one of the terminals of said machine and to an insulated terminal H, the discharge or load circuit being connected to the two said terminals.

Screen 2 in Fig. l is also connected to the terminal H of the machine.

The exciter in Fig. 1 comprises two small auxiliary generators 20 and 33 exciting each other and the construction of which is similar to that of the main generator but without a screen, that is to say, each of them comprises an inductor 2!, 3i and carriers 23, 24 and 33, 34 connected respectively to commutator contacts 26, 2'! and 35, 31 cooperating with brushes 28, Hand 38, 39. The inductor 2| of generator 29 is connected to brush '39 of generator 30 the potential of the inductor 3| of which is V and inductor 3| of generator 33 is connected to brush '29 'of generator 20 and to inductor l of the main generatorat -V potential. Brushes 28 and 38 or the auxiliary generators are both connected to the ground.

Between insulated terminal I l of the machine and inductor I is inserted a special resistance device the differential resistance of which chosen according to the above teachings, this device comprising in this embodiment an ohmic resister !2 in series with a glow discharge device diagrammatically shown as a point elec trode 13 located opposite to a plate electrode 14, the distance between point [3 and plate l4 being adjustable, as shown in the applicants copending application Ser. No. 77,317, filed February 14, 1949.

It may thus be seen that the two auxiliary generators form a self-exciting device producing a current proportional to the output voltage, the coefficient of proportionality or the ratio of the current produced by the exciter 20 to the potential across its terminals depending on the relation of the useful and the stray capacities. Such a device thus operates in fact as an exciter with a negative B coefiicient and a zero A coefiicient.

The generator shown in Fig. 2 is also associated with two small auxiliary generators. These auxiliary generators comprise the same members as in the above-described example of Fig. 1, these members being given thesame reference figures with the exception that screen 2 of the main generator, instead of being connected to the terminal II as in Fig. 1, is connected to brush 3!) of generator 30. This screen in Fig. 2 thus forms a further inductor the potential applied to which is U+V, the potential applied to inductor I being again -V. Thus the generator is of the double transfer type such as described in U. S. Patent No. 2,519,554.

It may be seen that each exciter is a machine of the Toepler type excited under a potential difierence V and having across its terminals a potential difference U+V. The current it produces is given by the equation:

A1 and B1 being positive and Al being larger than B1. Coefiicient B of each exciting machine, equal to B1A1, is therefore negative as required. Two special resistance devices are, of course, necessary, one of them l2, l3, I4 being inserted between inductor l at potential V and insulated terminal I! at potential {U as is the preceding case, the other resistor 42, 43, 44 being inserted between inductor 2! at potential U-l-V and ground Ill. It is of advantage that both resistance devices be similarly constructed and simultaneously and identically adjusted so as to practically maintain the symmetry of the two exciters.

In all cases the constant voltage delivered by the main machine is adjustable at will by vary ing the distance between points I3, 43 and the respective plates 14, 44-, that is, the potential difference for which resistance Z assumes the value l/B' which ensures the operation under constant voltage. It is sufiicient to vary the distance from point to plate of the glow discharge device to obtain a variation in the same direction of the constant voltage delivered by the main machine.

It may be advantageous in certain particular cases that the voltage of the generator, instead of being independent of the current delivered, shall increase or decrease slightly when the current increases. Such a result is directly obtained by slightly increasing or decreasing, according to result desired, the efiective resistance Z of the special resistance device or devices.

In the preceding embodiments the resistance device or devices are inserted between the output terminal H at potential U and the inductor l at potential -V. When potential U is very high it may be advantageou to collect, by means of a potential divider, only a constant fraction of U, such as lcU where k l, and to apply the potential difference 7cU+V instead of U+V across the resistance device. Care must then be taken that ZA be different from k. Factor is may even be made equal to zero, the resistance device then being inserted between a point of potential V and the ground but care must then be also taken that coefficient A be of a sufficient value, considering that ZB+1=0 no longer implies that dU=O if k=0 and A':0.

The theoretical study of stability show that it is generally to be preferred that the coefficient B of the machine be of positive sign, which is generally the case.

The above described embodiments are only given to show that there are practically usable means to give coefiicient B a negative value. However, such embodiments are only illustrative. For instance, within the scope of the invention, as defined in the following claims, an exciter might be substituted by any group of machines giving the same result, that is, having a negative B coefiicient.

WhatIclaimis:

l. Electrostatic generating apparatus comprising a conductive inductor member, a conductive carrier member, said inductor and carrier members being supported in insulated relation to each other and for relative movement therebetween into and out of inductive relation to each other, means connected to said inductor member for charging said inductor member at an excitation potential, means operatively connected to said carrier member and operable to establish connection of said carrier member to a terminal of said apparatus at a predetermined position of said carrier member in relation to said inductor member to deliver to said terminal a charge induced upon said carrier member by said inductor member in said relative movement of said members, and a leakage circuit connected between said inductor member and a terminal of said electrostatic generating apparatus, said leakage circuit including an eiiective resistance which varies with variation of the potential difference applied across said effective resistance to determine current flow therethrough such that the potential difference thereacross remains substantially constant.

2. Electrostatic generating apparatus comprising a conductive inductive member, a con ductive carrier member, said inductor and carrier members being supported in insulated relation to each other and for relative movement therebetween into and out of inductive relation to each other, means connected to said inductor member for charging said inductor member at an excitation potential, means operatively connected to said carrier member and operable to establish connection of said carrier member to a terminal of said apparatus at a predetermined position of said carrier member in rela tion to said inductor member to deliver to said terminal a charge induced upon said carrier member by said inductor member in said relative movement of said members, and a leakage circuit connected between said inductor member and a terminal of said electrostatic generating apparatus, said leakage circuit including a device providing for substantial variation of the current flowing therethrough with substantially constant potential drop thereacross.

3. Electrostatic generating apparatus comprising a generating conductive inductor member, a generating conductive carrier member, said inductor and carrier members being supported in insulated relation to each other and for relative movement therebetween into and out of inductive relation to each other, a generating output terminal, means connected to said inductor member for charging said inductor member at an excitation potential, means operatively connected to said carrier member and operable to establish connection of said carrier member to said output terminal at a predetermined position of said carrier member in relation to said inductor member to deliver to said output terminal a charge induced upon said carrier member by said inductor member in said relative movement of said members, and a leakage circuit connected between said in- 1 ductor member and said output terminal, said leakage circuit including a device providing for substantial variation of the current flowing therethrough with substantially constant potential drop thereacross.

4. Electrostatic generating apparatus as de 6 fined in claim 3 in which said leakage circuit includes an ohmic resistance in series with said device.

5. Electrostatic generating apparatus as defined in claim 3 in which said device in said leakage circuit comprises .a glow discharge device capable of carrying therethrough a current varying over a substantial range with a substantially constant potential drop thereacross.

6. Electrostatic generating apparatus as defined in claim 5 in which said glow discharge device comprises a plate anode and a pointed cathode.

'7. Electrostatic generating apparatus comprising a generating conductive inductor memher, a generating conductive carrier member,

said inductor and carrier members being sup.-

ported in insulated relation to each other and for relative movement therebetween into and out of inductive relation to each other, a generating output terminal, an auxiliary electrostatic generator having an inductor memberand a carrier member supported in insulated relation to each other and for relative movement there etween into and out of inductive relation to each other, means operatively connected to said carrier member of said auxiliary generator and operable to establish connection of said auxiliary carrier member to said generating inductor member for delivering to said generating inductor member a charge induced upon said auxiliary carrier member by said auxiliary inductor member in said relative movement thereof for charging said generating inductor member with an excitation potential, means operatively connected to said generating carrier member and operable to establish connection of said generating carrier member to said output terminal at a predetermined position of said generating carrier member in relation to said generating inductor member to deliver to said output terminal a charge induced upon said generating carrier member by said generating inductor-member in said relativemovement of said members, a leakage circuit connected between said generating inductor member and said output terminal, said leakage circuit including a device providing for substantial variation of the current flowing therethrough with substantially constant potential drop thereacross, and an auxiliary leakage circuit connected between said auxiliary inductor member and a terminal of said electrostatic generating apparatus, said auxiliary leakage circuit including a device providing for substantial variation of the current flowing therethrough with substantially constant potential drop thereacross.

3. Electrostatic generating apparatus as defined in claim '2 in which said auxiliary leakage circuit is connected between said auxiliary inductor member and ground.

9. Electrostatic generating apparatuscomprising a conductive inductor member, a conductive carrier member, said inductor and carrier mem-- bers being supported in insulated relation to each other and for relative movement therebetween into and out of inductive relation to each other, means connected to said inductor member for charging said inductor member at an excitation potential, means operatively connected to said carrier member and operable to establish connection of said carrier member to a terminal Of said apparatus at a predetermined position of said carrier member in relation to said inductor member to deliver to said terminala charge induced upon said carrier member by said inductor member in said relative movement of said members, and a leakage circuit connected between said inductor member and a terminal of said electrostatic generating apparatus, said leaka e circuit including an effective resistance which varies with variation of the potential difference applied across said effective resistance to determine current flow therethrough such that the potential difference thereacross remains substantially constant, said effective resistance being Z and varying non-linearly as a function of the potential difierence thereacross, Z being opposite in sign to a coefficient B which expresses the ratio of the current I supplied by said means forcharging said inductor member to the difference of potential V supplied by said charging means, Z being equal to 1/B when the potential difference across Z is substantially U+V where U is the potential diiierence across the terminals of the electrostatic generating apparatus, Z being greater than -1/B when the potential difference across Z is les than U+V.

l0. Electrostatic generating apparatus comprising a generating conductive inductor member, a generating conductive carrier member, said inductor and carrier members being supported in insulated relation to each other and for rela tive movement therebetween into and out of inductive relation to each other, a generating output terminal, means operatively connected to said carrier member and operable to establish connection of said carrier member to said output terminal at a predetermined position of said carrier member in relation to said inductor member to deliver to said output terminal a charge induced upon said carrier member by said inductor member in said relative movement of said members, an auxiliary electrostatic generator having an inductor member and a carrier member supported in insulated relation to each other and for relative movement therebetween into and out of inductive relation to each other, means operatively connected to said carrier member of said auxiliary generator and operable to establish connection of said auxiliary carrier member to said generating inductor member for delivering to said generating inductor member a charge induced upon said auxiliary carrier member by said auxiliary inductor member in said relative movement thereof, means connected to said auxiliary inductormember for chargin said auxiliary inductor member at a potential to provide an excitation potential upon said generating inductor member in the charge delivered thereto by said auxiliary carriermember, and a leakage circuit connected between said auxiliary inductor member and a point of substantially constant potential of said electrostatic generating apparatus, said leakage circuit including a device providing for substantial variation of the current flowing therethrough with substantially constant potential drop there across.

11. Electrostatic generating apparatus comprising a generating conductive inductor member, a generating conductive carrier member, said inductor and carrier members being supported in insulated relation to each other and for relative movement therebetween into and out of inductive relation to each other, a generating output terminal, means operatively connected to said carrier member and operable to establish connection of said carrier member to said output terminal atapredetermined position of said carrier member in relation to said inductor member to deliver to said output terminal a charge induced upon said carrier member by said inductor member in said relative movement of said members, an auxiliary electrostatic generator having an inductor member and a carrier member supported in insulated relation to each other and for relative movement therebetween into and out of inductive relation to each other, means operatively connected to said carrier member of said auxiliary generator and operable to establish connection of said auxiliary carrier member to said generating inductor member for delivering to said generating inductor member a charge induced upon said auxiliary carrier member by said auxiliary inductor member in said relative movement thereof, means connected to said auxiliary inductor member for charging said auxiliary inductor member at a potential to provide an excitation potential upon said generating inductor member in the charge delivered thereto by said auxiliary carrier member, an additional conductive inductor member associated with said generating inductor member and said generating carrier member and disposed for movement of said generating carrier member into and out of inductive relation thereto concomitantly with movement of said generating carrier member out of and into inductive relation to said generating inductor member, said additional inductor member being electrically connected to said auxiliary inductor member, and a leakage circuit connected between said electrical connection and a point or substantially constant potential of said appa- 10 ratus, said circuit including a device providing for substantial variation of the current flowing therethrough with substantially constant potential drop thereacross.

12. Electrostatic generating apparatus as defined in claim 10 in which said means connected to said auxiliary inductor member for charging said auxiliary inductor member comprises a supplemental electrostatic generator having an inductor member and a carrier member supported in insulated relation to each other and for relative movement therebetween into and out of inductive relation to each other, and means operatively connected to said carrier member of said supplemental generator and operable to establish connection of said supplemental carrier member to said auxiliary inductor member for delivering to said auxiliary inductor member a. charge induced upon said supplemental carrier member by said supplemental inductor member in said relative movement thereof.

13. Electrostatic generating apparatus as defined in claim 1 in which as the potential difference across said effective resistance increases and decreases said effective resistance decreases and increases concomitantly with increase and decrease in the current flow therethrough so that the potential diiference across said resistance remains substantially constant.

NOEL FELICI.

No references cited. 

